1. Field of the Invention
This invention relates to a small-size printer, and more particularly to a latch mechanism for a small-size printer which is capable of performing a printing operation with a rotatable type drum secured in a print position by impacting a hammer towards the type drum against recording paper.
2. Description of the Related Art
A small size printer is well known as an external recording means for numerical data output from such devices as a cash register or a calculator, being of relatively simple mechanical structure and capable of printing any desired characters or symbols at high speed.
This type of small size printer comprises a plurality of type drums of multiple digits, each of which has a plurality of types on its outer peripheral. Each type drum is independently and rotatively supported by a type drum shaft. In the reset state, the type drums and the type drum shaft are latched together by a constant torque clutch, so that all of the type drums are rotated with the type drum shaft at a predetermined position. Consequently, although each of the type drums rotate with the type drum shaft, when the type drum is locked, it is possible to halt a type drum at a position where the desired type on the drum comes to the print position.
To this end, each type drum has a lock groove wheel disposed adjacently to the type drum and is provided with a lock lever which comprises a lock claw on its upper end for latching the lock groove wheel. As described above, since the lock claw of the lock lever latches the lock groove wheel to stop the type drum, the apparatus is now ready for a line print operation.
That is, the lock claw of the lock lever latches a groove of a lock groove wheel which corresponds to a desired type on the type drum when the type drum comes to the predetermined print position opposite to the printing hammer. With the type drum secured in the print position, an impact operation of the hammer is performed to the type drum through a recording paper.
The existing type drum latch mechanism as described above is configurated such that, when not printing, a lock lever which is disposed on the opposite side of the printing portion formed on the outer peripheral of the type drum and is constantly biased by a lock lever spring towards the type drum is held in its initial non-print position remote from the type drum, while, at the time of type selection, the lock claw of the lock lever latches the lock groove wheel of the type drum with the aid of the spring force.
With this existing latch mechanism for small-size printers, however, there is the problem that since a latching or releasing operation of the lock lever is performed by an electromagnet provided for each of the type drums of plural digits, the space and production cost occupied by these plural electromagnets and thus the total cost increased remarkably, preventing the reduction in size and cost of the apparatus.